Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing my new design;

FIG. 2 is a second image thereof;

FIG. 3 is a third image thereof; and,

FIG. 4 is a fourth image thereof.

The outer perimeter broken line depicting the display screen or portion thereof throughout the drawings is for environmental purposes only and forms no part of the claimed design. The remaining broken lines in the drawings illustrate portions of the transitional graphical user interface which form no part of the claimed design.

The appearance of the graphical user interface sequentially transitions between the images shown in FIGS. 1-4. The process or period in which one image transitions to another forms no part of the claimed design. 

CLAIM I claim the ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 